octeontx2-af: add read back of AF_BAR2_SEL register

commit 4687119b1a36d8bc52b8c8c3ade81d642b3e0b20 from
git@git.assembla.com:cavium/WindRiver.linux.git

Adds the code to read back of CPT/SSO/AF_BAE2_SEL register to confirm
the write has done to it as per HW requirement, before accessing the LF
registers through BAR2_ALIAS.

Signed-off-by: Srujana Challa <schalla@marvell.com>
Change-Id: Ia4f309328ba33354eddb3c38d4a0b0a8c9c0b535
Reviewed-on: https://sj1git1.cavium.com/c/IP/SW/kernel/linux/+/86397


Reviewed-by: Jerin Jacob Kollanukkaran <jerinj@marvell.com>
Tested-by: sa_ip-sw-jenkins <sa_ip-sw-jenkins@marvell.com>
Signed-off-by: Ruiqiang Hao <Ruiqiang.Hao@windriver.com>